As development has continued on the Magnetically-confined Anode Plasma (MAP) ion beam source, now the subject of U.S. Pat. No. 5,525,805, certain improvements have been made that are the subject the present patent application. By way of background, the MAP ion beam source, also known as the MAP ion diode or MAP diode, has been combined with a high energy, short pulse power supply to create high energy, short duration, repetitively pulsed ion beams that can be employed in several ways. Chief among them are, for metal surfaces, increased hardness, smoothness, corrosion resistance and, for polymers, increased cross-linking and toughness. The particular construction of this MAP ion diode is such that it is able to be repetitively pulsed for long periods of time and thereby have broad commercial applications. Pulsed ion sources known prior to that covered by U.S. Pat. No. 5,525,805 could not be repetitively pulsed in this fashion and suffered as well from ion beam rotation and dispersion problems caused by the configuration of their magnetic coil components.
The MAP ion diode of U.S. Pat. No. 5,525,805 and the present MAP ion beam source have many of the same construction details. An ionizable substance, typically a gas, is introduced at a point on the central axis 11 of the device through a puff valve 14 as seen in FIG. 1. This puff valve is electrically controlled to open in approximately 25-50 .mu.sec, producing a puff of gas that arrives at a radius of 10 cm 50-150 .mu.sec later in the evacuated interior of the device. The puff valve in the present ion beam source comprises a Belleville shape conical diaphragm 12 made of beryllium-copper that seats against 2 O-rings, not shown, and is driven open by a 6 kA, 20 .mu.sec rise time pulse through a three turn coil 13 that flattens the diaphragm, allowing the gas trapped in the plenum between the O-rings to escape into and travels radially outwards through a passageway 14. The restoring force on the diaphragm and/or its contact with the inner anode flux excluder 16 causes it to return to the initial closed position. The passageway is designed to conduct the gas puff at supersonic speed to an ionization region 23 located behind an annular opening 24 in the anode electrode 16, 17 of the ion beam source 10. Both the anode electrodes 16, 17 and the cathode electrodes 18, 19 are disposed in radial fashion about the central axis and form an accelerating gap there between. The ionization chamber has a rear wall that contains fast magnetic coils 15. Slow magnetic coils 20 are located in the cathode electrode on each side of the annular opening 21.
The fast coils and the slow coils work together to ionize the gas into a plasma and to hold the plasma at the annular gap 24 in the anode electrode assembly 16, 17. Once the plasma is at the annular gap, the main power pulse from the pulsed power supply system is delivered to the anode electrode, and the ions in the plasma are accelerated in the accelerating gap between the anode and the cathode (held at ground) and out of the ion beam source through an annular gap 21 in the cathode electrode to interact with the material of interest, a metal or polymer surface for example. The direction of the accelerated ions is shown by the lines 22.